Approach to 6a-epipretazettine and 6a-epiprecriwelline via an intramolecular 2-azaallyl anion cycloaddition reaction

Article abstract of DOI:10.1021/jo00098a026

An intramolecular 2-azaallyl anion cycloaddition with a diene produced the 2,3,4,6,7,7a-hexahydroindole 33 with complete control of relative stereochemistry, thus providing the first example of the use of such a cycloaddition in an approach to a relatively complex target molecule. The 2-azaallyl anion was generated by tin-lithium exchange of the (2-azaallyl)stannane 32. The stannane was prepared by a convergent route using a Stille coupling of the vinyl bromide 14 with the vinylstannane 28, providing the diene 29. An unexpected isomerization occurred in the Stille coupling. Transformation of the cycloadduct 33 to the allylic methyl ethers 36 and 37 produced potential precursors of 6a-epiprecriwelline (4) and 6a-epipretazettine (3), respectively. The inability to carry out an oxidative desilylation thwarted the completion of the syntheses of these alkaloids.